Fabric softener compositions, especially concentrated and/or superconcentrated, are dispersions of positively charged vesicles containing the softener active. These vesicles are believed to be comprised of alternating concentric layers of water and lamellar cationic bilayers, so-called lamellar droplets. The presence of lamellar droplets in a fabric-softening composition can be detected by methods known to persons skilled in the art like optical techniques, rheometrical measurements, X-ray diffraction and electron microscopy. The droplets consist of an onion-like configuration of, as pointed out above, concentric bilayers of molecules of fabric-softening material with entrapped water or electrolyte solution, the so-called aqueous phase.
A well-appreciated fabric softener product exists of physical stability and desirable flow properties combined in one system.
However, upon storage the dispersions above-mentioned are thickening and eventually gelling. The reason for this phenomenon is not yet clear. There are, at least, two theoretical possibilities: the lamellar vesicles are increasingly interconnecting with time and eventually (1) form an infinitely inter-connected vesicle network or gel, or (2) change from a lamellar vesicle to a two-phase lamellar phase in which gelation may occur.
Regardless of the mechanism, gelation probably will be avoided as long as the vesicles are kept separated from each other.
It is well-known that two factors mainly determine the viscosity and stability of the fabric softening composition. First of all, it is the volume (fraction) of the dispersed lamellar phase in the composition and secondly it depends on the state of aggregation of these droplets. In general, the higher the volume (fraction) of the droplets (dispersed lamellar phase), the higher the viscosity which, if too high, results in an unpourable product. One way to solve this problem is using electrolytes whereby apparently the size of the lamellar vesicles is reduced and, as such, increases the inter-vesicle distances preventing aggregation/gelation.
However, the stability of other components in the fabric-softener composition is affected using higher electrolyte levels.
So there are limits to the amount of fabric softening material and electrolyte to be used whilst still having an acceptable product. There is a continued need for more concentrated, sometimes superconcentrated, fabric softening compositions for convenience and cost reduction purposes. The problem to be solved is that these high concentrations of softener active in the compositions must have an acceptable stability and at the same time pourability upon use.